In an imaging apparatus, a plurality of lenses are coaxially provided, and when any of the respective lenses is displaced in optical directions thereof, an optical zoom is achieved. Later-described first to fifth conventional arts are well known as a technique for displacing a lens.
The first conventional art is disclosed in Japanese Unexamined Patent Publication JP-A 2001-242366. In the first conventional art, a screw rod which rotates by means of an electromagnetic motor; and a guide shaft are arranged in parallel with each other. A lens holder has a holding portion which holds a lens, and a threaded portion into which the screw rod is inserted and threadably engaged. The lens holder is configured so that rotation about the screw rod is controlled by the guide shaft. When the screw rod rotates by means of the electromagnetic motor, the lens holder is displaced along the screw rod.
In the first conventional art as just described, the lens holder maintains a posture thereof with the aid of the screw rod and the guide shaft. In the case where the screw rod contributes to maintenance of the posture of the lens holder as above, friction resistance between the screw rod and the threaded portion becomes larger. The increase in the friction resistance between the screw rod and the threaded portion impedes the rotation of the screw rod or stops the rotation of the screw rod. Accordingly, the first conventional art as above has such a problem that the lens held by the lens holder cannot be displaced smoothly. Further, a driving force-transmitting member such as the screw rod or a stick member coupled to a piezoelectric element requires allowance relative to a member for positioning or guiding the driving force-transmitting member. It is therefore difficult to maintain the posture of the lens holder with high accuracy in the case where the driving force-transmitting member contributes to the maintenance of the posture of the lens holder.
FIG. 12 is a perspective view schematically showing a configuration of a lens unit of the second conventional art. In the second conventional art, a first guide member 1 and a second guide member 2 are arranged in parallel with each other.
A first lens holder 3 has a first holding portion 5 which holds a first lens 4; a first main sliding portion 6; and a first sub sliding portion 7. The first lens holder 3 is provided so as to be displaceable along the first and second guide members 1 and 2, as being guided by the first guide member 1 at the first main sliding portion 6 and guided by the second guide member 2 at the first sub sliding portion 7.
The second lens holder 8 has a second holding portion 10 which holds a second lens 9 coaxially with the first lens 4; a second main sliding portion 11; and a second sub sliding portion 12. The second lens holder 8 is provided so as to be displaceable along the first and second guide members 1 and 2, as being guided by the first guide member 1 at the second main sliding portion 11 and guided by the second guide member 2 at the second sub sliding portion 12.
In the second conventional art, the first main sliding portion 6 is formed so as to extend along the first guide member 1 in order to slide the first main sliding portion 6 smoothly on the first guide member 1. The first main sliding portion 6 becomes more balanced and therefore slides more easily as being longer along the first guide member 1. Moreover, the second main sliding portion 11 is formed so as to extend along the first guide member 1 in order to slide the second main sliding portion 11 smoothly on the second guide member 2. The second main sliding portion 11 becomes more balanced and therefore slides more easily as being longer along the first guide member 1. The second main sliding portion 11 is provided so as to protrude on a first holding portion 5-side relative to the second lens 9.
In the second conventional art as above, the first main sliding portion 6 and the second main sliding portion 11 are guided by a guide member in common and moreover, the second main sliding portion 11 protrudes on the first holding portion 5-side relative to the second lens 9. Accordingly, the first main sliding portion 6 and the second main sliding portion 11 undesirably interfere with each other when the first lens 4 and the second lens 9 are brought close to each other, causing a problem that the first lens 4 and the second lens 9 cannot be sufficiently close to each other.
FIG. 13 is a perspective view schematically showing a configuration of a lens unit of the third conventional art. FIG. 14 is a side view seen in an arrow 15 direction in FIG. 13. The lens unit of the third conventional art is similar to the lens unit of the second conventional art and therefore, the same parts will be denoted by the same symbols to omit descriptions thereof.
In the third conventional art, the first main sliding portion 6 is provided so as to protrude on a side opposite to the second holding portion 10 relative to the first lens 4, and the second main sliding portion 11 is provided so as to protrude on a side opposite to the first holding portion 5 relative to the second lens 9. Both ends of the first guide member 1 and both ends of the second guide member 2 are fixed to a housing 16.
In the third conventional art as above, the first main sliding portion 6 is provided so as to protrude on the side opposite to the second holding portion 10 relative to the first lens 4, and the second main sliding portion 11 is provided so as to protrude on the side opposite to the first holding portion 5 relative to the second lens 9. Accordingly, the first main sliding portion 6 and the housing 16 undesirably interfere with each other and the second main sliding portion 11 and the housing 16 undesirably interfere with each other when the first lens 4 and the second lens 9 are brought away from each other, causing a problem that the first lens 4 and the second lens 9 cannot be sufficiently away from each other.
The fourth conventional art is disclosed in the Japanese Unexamined Patent Publication JP-A 2002-131611. In the fourth conventional art, first to third guide shafts are arranged in parallel with each other. A first movable lens frame has a first holding portion which holds a first lens; a first guide bush portion which slides on the first guide shaft; and a first rotation stop portion which slides on the second guide shaft. A second movable lens frame has a second holding portion which holds a second lens; a second guide bush portion which slides on the second guide shaft; and a second rotation stop portion which slides on the third guide shaft. The first guide bush portion protrudes on a second holding portion-side relative to the first lens. The second guide bush portion protrudes on a first holding portion-side relative to the second lens.
In the fourth conventional art as above, the second guide bush portion and the first rotation stop portion slide on the guide shaft in common and moreover, the second guide bush portion protrudes on the first holding portion-side relative to the second lens. Accordingly, the second guide bush portion and the first rotation stop portion undesirably interfere with each other when the first lens and the second lens are brought close to each other, causing a problem that the first lens 4 and the second lens 9 cannot be sufficiently close to each other.
The fifth conventional art is disclosed in the Japanese Unexamined Patent Publication JP-A 2002-131611 as in the case of the fourth conventional art. In the fifth conventional art, first to fourth guide shafts are arranged in parallel with each other. A first movable lens frame has a first holding portion which holds a first lens; a first guide bush portion which slides on the first guide shaft; and a first rotation stop portion which slides on the second guide shaft. A second movable lens frame has a second holding portion which holds a second lens; a second guide bush portion which slides on the third guide shaft; and a second rotation stop portion which slides on the fourth guide shaft. The first guide bush portion protrudes on a second holding portion-side relative to the first lens. The second guide bush portion protrudes on a first holding portion-side relative to the second lens.
The fifth conventional art as above can solve the problem of the fourth conventional art, but has a problem that mounting errors for respective guide shafts accumulate to decrease positioning accuracy of the lenses since the first guide bush portion and the second guide portion slide on the different guide shafts and in addition, the first rotation stop portion and the second rotation stop portion slide on the different guide shafts.